The present invention relates to a rear-surface projection-type video display.
In recent years, developments are remarkable upon a large and flat video display apparatus, and in the place of the projection-type video display apparatus, which are widely used, conventionally, video display apparatuses come to be spread, widely, applying so-called a flat panel, such as, a plasma display panel (PDP), a large-size liquid crystal panel (LCP), and further an organic EL panel, etc., for example. Accompanying this, upon the projection-type video display apparatus, it is strongly demanded to be superior of portability and cheaply producible, as well as, further large-sizing of a display surface thereof, with using the characteristics thereof profitably, i.e., by taking a use thereof in an educational field or in a conference room, etc., into the consideration thereof.
On the other hand, in the conventional video display apparatus of projection-type, in particular, in a rear-surface projection-type video display apparatus of projecting an image or picture from a rear surface of a screen, generally, as is shown in Japanese Patent Laying-Open No. 2008-216797 (2008), for example, there are provided an optical engine for projecting a visual light and a plural number of mirrors for enlarging that visual light projected and also for entering it on the rear surface of the screen, within a housing, building up an cuter configuration of that apparatus. Also, as is disclosed in Japanese Patent Laying-Open No. 2009-168871 (2009) and Japanese Patent Laying-Open No. 2009-163163 (2009), the video projection apparatus is provided within an inside of that apparatus housing, and by means of a rear surface mirror attached on a rear surface of that apparatus housing, the visual light projected therefrom is enlarged and entered on the rear surface of the screen.
As was mentioned above, in the conventional video display apparatus of projection-type, in particular, in the rear-surface projection-type video display apparatus of projecting the visual from the rear surface of the screen, since a transmission-type screen (hereinafter, only “transmission screen”) for displaying a picture on a front surface of a video display surface is attached on a front surface of the housing, building up the outer configuration of the apparatus as was mentioned above, a Fresnel lens attached on a back surface of that transmission screen is provided for transmitting the visual light received from the back surface therethrough, and commonly, it is made up with a plural number of Fresnel surfaces, which are formed in a circle ring manner (a circular Fresnel lens). Further, in the Patent Laying-Open No. 2008-216797 (2008), in particular, there is disclosed a refraction type Fresnel lens, height of which is so determined that stray lights in a predetermined area or region of Fresnel angle are emitted towards to the front surface facing to a viewer side.